1. Field of the Invention
The present invention relates to a recording tape cartridge, and more particularly to an improvement of a tape guide piece used in a three piece type tape cartridge wherein a top case half, a bottom case half and a tape guide piece are separately molded and they are assembled together.
2. Description of the Prior Art
An example of the three piece type tape cartridge mentioned above is shown in FIG. 1 to FIG. 3, wherein three members of a tape cardridge including a top case half 1a, a bottom case half 1b and a tape guide piece 10 are molded separately. The tape guide piece 10 has its one side (front side) with formed guide ribs 16 facing to a recording and reproducing head insertion window 6 (referred to as recording head insertion window hereinafter) and guide ribs 15 and 17 facing to an erasing head insertion window 7 and a pinch roller insertion window 8 and has its other side (rear side) as defined concave portions 30 on both left and right regions The tape guide piece 10 is molded as a separate body from the top and bottom case halves 1a and 1b in order to enhance the abrasion proof property and to improve the accuracy of work of the respective guide ribs 15, 16 and 17.
As means for positioning the tape guide piece 10 relative to the top and bottom case halves 1a and 1b, there are provided bosses 27 extending in a vertical direction between the guide ribs 16 and 17 with standard positioning holes 12 defined in the respective bosses 27 so as to extend in a vertical direction and a central hole 28 defined in the top and bottom case halves 1a and 1b between the bosses 27, thereby causing the bosses 27 to be inserted in installing holes 29 which are situated at positions corresponding to the conventional positioning standard holes and causing the central hole 28 to be fitted with a screw boss 22 projected on the top and bottom case halves 1a and 1b, so that the tape guide piece 10 is regulated in terms of position in the front and rear directions and left and right directions in the cartridge.
In the conventional tape guide piece 10 mentioned above, since the parts of the tape guide piece 10 thinned by the concave portions 30 lack mechanical strength, a reinforcing rib 31 is attached only at the lower end of the concave portion 30, and moreover the thinned portions are reinforced by the bosses 27. In the contrivance of attaching the reinforcing rib 31 only to the lower end of the concave portion 30, the vertical cross sectional shape of the tape guide piece 10 becomes asymmetrical in connection with the top and bottom direction of the tape guide piece 10, whereby in molding the tape guide piece 10, the balance of the flow of the molten resin is negatively affected and there tends to occur deformation, curving, bending and torsion due to the shrinkage of the molded tape guide piece after molding.